The UK Private Mobile Radio 446 specification defines type approved radio transceivers and
aerials. The
public can buy and use any radio transceiver which is type approved to the
PMR446 specification. Such radios use a UHF band of 8 radio channels.
Such PMR446 radios can also be legally used in some other European countries.

PMR446s can be used by the public for recreational purposes and by companies
for business purposes. They can be used by huge men in dark uniforms with
silver buttons and also by small girls with pigtails, freckles and pink dresses.

The
concept of licence-free means that almost anybody can use these radios for
almost any purpose.

As there are only 8 radio channels and zillions of people in the UK who own
PMR446s, there could be a problem in trying to get a word in edgeways. The
huge men in dark uniforms with silver buttons may think that they are more
important than the small girls with pigtails, freckles and pink dresses.
They aren't.

Anybody (especially a business) who uses PMR446 radios must
realise that anybody in range can hear what is said and that nobody has an
exclusive right to use any of the 8 channels. While using your radio,
others may suddenly appear on "your" channel. Tough. If
you don't like it, pay £1,000 for a pair of PBR radios.

There are
only two ways in which such a licence-free system can work. The first is
to severely limit the radio range of every radio. The second is for users
to accept that the channels are shared and to try not to use a channel which is
already in use.

Asking an expert the range of a particular radio system often results in a
very vague reply. It isn't because of lack of knowledge. It is
because many things can alter the range.

PMR446s are often advertised as
having a maximum range of one or two miles. In the UK, laws state that
advertising must be honest, accurate and not misleading. PMR446s therefore
do have a maximum range of a mile or two. On a sunny day. With the
wind behind them. As long as you use them whilst standing on one leg and
holding your left finger in your right ear and winking. At other times,
they couldn't transmit themselves out of a wet paper bag.

Situations which
could severely limit the range include being in a building, in a street with
tall buildings, among trees and among crowds of people. Being inside a car
does diminish the range slightly, but not severely.

The PMR446 range is
therefore between one hundred yards and two miles. If you can see the
other radio, you can probably talk to it. If you can't see it, you may or
may not be able to talk to it.

Like all type approved equipment, it isn't type approved any more if you
modify it. The PMR446 specification is a maximum of 0.5 Watts of effective
radiated power. If the aerial has a gain of 1, its transmitter can have a
power of 0.5 Watts. If the aerial has a gain of 10, the transmitter must
be only 0.05 Watts.

The European PMR446 licence-free specification says that the radios
can't have the facility to connect to huge aerials as that would increase their
range. Legally, you can't even delve inside the radio to connect a pair of
headphones from the loudspeaker connections as that would be modifying the radio
and it would no longer be to specification PMR446.

PMR446s therefore have a
built-in aerial and no socket to which an external aerial can be
connected. They may or may not have sockets for an external microphone or
headphones. PMR446s linked via the internet connect via the provided
microphone and headphone sockets.

Radios must only be of the hand portable
variety. They can't be the mobile radio variety. They can still be
used in cars.

But previously it said that there are only 8 channels? It depends on what you understand by
the term "channel". There are 8 radio channels, which means
there are 8 radio frequencies with a bandwidth for speech. Within a small
distance, there can be only 8 simultaneous exclusive conversations.

The use of
CTCSS can appear to provide more channels, but it doesn't. What it does do
is provide the convenience of appearing to have more channels. It doesn't
really matter what CTCSS stands for as long as it works. In case you want
to impress your friends with official geek radio gobbledygook, it is Continuous
Tone Coded Squelch System and is sometimes called sub-audible tones. If
you use the hyperlink at the bottom of this page, you'll see that Ofcom believes
that CTCSS stands for different words.

If a PMR446 radio has CTCSS, it transmits a
secret inaudible sound whenever somebody speaks on the radio. Pedants may
say that a sound can't be inaudible as that is an oxymoron. What these
morons don't know is that CTCSS has existed for years and it works.

If the
receiving radio also has CTCSS and is using the same secret inaudible sound
(sorry about this), the loudspeaker works as expected and the voice at the
transmitter end is heard. "So what?", you ask. Well the
use of CTCSS in an area of heavy PMR446 usage can improve things.

Suppose that
you are in a park where a local pop group will be giving a free
performance. There is an audience of 1,000 people. Many are parents
who have a PMR446 and have given their children a PMR446 so that they can run
about in the park whilst still keeping in contact with Mam and Dad.
Suppose that 50 adults have radios and 50 children have radios. At any one
time there is a possibility of requiring 50 simultaneous radio conversations but
there is only the possibility of 8 simultaneous conversations.

This can work
if they all take it in turn to have their conversations such as, "Come back
to your seat. The band starts playing in 10 minutes.", "Certainly
Daddy dear. And I will bring you an ice-cream which I bought with that
£20 note which you gave me." It is likely to be quite messy, but it can
eventually work.

If all of the 100 people are using PMR446 channel 1 because
that it what they normally use, it could take a while and the band will have
stopped playing and have been in the pub for hours before all of the kids get
all of the messages.

If a random spread of channels and a random spread of
CTCSS tones (but the CTCSS tones must be in pairs) is used, things may sound
better. Instead of everybody hearing anybody else who is using the same channel,
they only hear anybody who is using both the same radio channel AND the same CTCSS
tone.

If you think that the channel is free to use as you hear nothing, when
you press the transmit button, you won't actually transmit if your radio is
receiving a signal at the time. This stops you interfering with other
people's signals and vice versa.

CTCSS using the same sub-audible tones at the transmit end and the receive
end can give the appearance of having many channels. It certainly prevents
you having to listen to other users of the same radio channel. It can also merely
mask the fact that the radio channels are in heavy use as you can't hear
anything.

CTCSS is of most use with light or medium radio traffic. With heavy
radio traffic conditions, as you can't hear all the other stations, you won't
realise why your friend, colleague or relative isn't answering you.